Droplets in turbulent flow

Clustering in turbulent droplet ensembles: the role of phase transitions

Description:Multiphase flows in which a large number of small droplets is dispersed in a gas, play an important role in variety of technological applications- thermal processing in food manufacturing, air pollution control, energy conversion industry. Heat conductivity of droplets and phase transition will affect the heat transfer of the flow, that is widely applied in turbulent spray cooling.

We examine the effect of two-way coupling and phase-transition on Nusselt number and droplets’ concentration within turbulent channel flow. Nusselt number shows the influence of droplets on the heat transfer of the whole mixture, while the concentration of the droplets refers to the effect of turbophoresis.

Turbophoresis is the effect of migration of the particles in the particle-laden turbulent channel flow to the areas of decreasing turbulence level.

Mathematical modelThe carrier phase is considered to be compressible and Newtonian fluid. The compressibility assumption becomes very important in case phase transitions are taken into consideration. In fact, if the carrier phase is assumed to be strictly incompressible then the inclusion of evaporation and condensation is subject to the condition that all instantaneous changes in the local mass-density of air and water vapor cancel each other precisely throughout the domain. In this project the incompressible model is complemented by a fully compressible description, which allows to quantify the consequences of non-constant mass-density of the carrier gas.

The behavior of the carrier phase is described by the continuity equation, Navier-Stokes equation and energy conservation equation. Particles and droplets are described by the set of ordinary differential equations. The two-way coupling is implemented via momentum, energy and mass source terms.